Where do I use the command

From bitcoin-qt use Help -> Debug Window then click on the Console tab where you can issue the "importprivkey" command (if your wallet has been encrypted you'll need to *unlock* it first).

BTW - did you solo mine that 50 BTC back in 2009?

Really? You have generated the private Key to this address?

Don't forget to post if this actually works.

Also Post if it doesn't. I'm curious.

Just how likely is it to generate an existing address? I thought it was next to impossible.

Was this a brainwallet based upon a passphrase?

Don't think so. single wallet.

JimmyFL but the owner hasn't used it for years. finders keepers

click on third icon.

then it will show wallet import tab.

thanks, I see it now. Your sig address is OK?

Maybe both the owner of this address (afaik it could be one of the few people with whom Satoshi conversed about bitcoin in 2009) used a similar method with a predictable output to generate an address as ssbtoday with bitaddress: https://github.com/pointbiz/bitaddress.org/blob/master/bitaddress.org.html

This would also mean that other people who used bitaddress at some point (not sure if all versions would be affected and if it is a randomness issue).

For now, I refuse to believe a collision occured until OP proves he has access to the coins.
 

Some day, you'll lose your private keys. Some random exploit, virus, perhaps somebody ripping you off; whatever the case, you'll come back to this forum demanding justice and doing everything you can to find the robber, completely outraged. How dare they stealing my coins you'll think. When that happens, I'll link you to this thread and remind you how you once were the robber who stole 50 BTC. Have a good day